It is disclosed in U.S. Pat. No. 4,400,340 and U.S. Pat. No. 4,426,502 that ring-opening polymerization of a cycloolefin containing norbornene moiety, e.g. dicyclopentadiene (called "DCP" hereinafter), in the presence of a metathesis polymerization catalyst system produces a crosslinked polymer containing olefinic groups in the main chain
Said U.S. Pat. No. 4,400,340 and U.S. Pat. No. 4,426,502 disclose the production of a molded article by injecting a reactive liquid mixture comprising norbornene-type monomer such as DCP and a metathesis polymerization catalyst system into a mold in which said liquid mixture is metathesis polymerized in bulk (called "RIM process" hereinafter). RIM process is a low pressure one-step or one-shot injection of a liquid mixture into a closed mold where rapid polymerization occurs resulting in a molded article. Thus, there are easily produced large-sized molded articles from DCP and the like by RIM process. The molded articles have been taken notice from the industrial point of view since they have attractive physical properties as balanced in stiffness and impact resistance.
The cross-linked DCP polymer and molded articles, however, are composed of hydrocarbon polymer. Thus, they are flammable and will burn continuously when ignited. Further, the polymer and molded articles produced from DCP have low softening points generally below 100.degree. C. Those undesirable characteristics of the DCP polymer and molded articles often limit the use of them.
On the other hand, there has been proposed the addition of flame retardants, such as decabromodiphenylether and the like, to the polymerizable DCP mixture. However, the addition of such flame retardants often produces troubles in the metathesis polymerization of DCP. That is, the metathesis polymerization catalyst system is generally highly reactive and often reacts with the flame retardants to reduce its catalytic activity. Furthermore, even if such flame retardants do not reduce the activity of the metathesis catalyst system, such flame retardants have high density and are generally insoluble and less dispersible in monomer solutions. The insolubility and less-dispersibility often cause less-workability in the molding process. Further, the addition of flame retardants often impairs the mechanical properties of the polymer and molded article.
In addition, there are some proposals to raise the softening point of DCP polymer. Among of them is included the copolymerization of DCP with other metathesis polymerizable monomers having bulky cyclic structure, such as dimethanooctahydronaphthalene, dimethanohexahydronaphthalene and the like. Such comonomers, however, do not provide the polymer with flame retardancy and improved solvent resistance.
Other methods to raise the softening point are the introduction of polar groups such as amido-, nitrile- and imido-groups into DCP polymer. However, amide groups often inhibit the metathesis polymerization reaction, and nitrile- and imido-groups tend to retard the polymerization reaction.
Now, we have found that metathesis polymerizable halogen-containing cycloalkenes can be readily copolymerized with DCP without inhibiting the metathesis polymerization reaction and can provide DCP-polymer with flame retardancy as well as raised softening point.
Therefore, it is an object of the present invention to provide a metathesis polymerized cross-linked halogen-containing copolymer having flame retardancy and raised softening point.
A further object is to provide a process for producing said copolymer. Another object is to provide a process for producing a molded article comprising the copolymer. A further object is to provide a polymerizable composition used for producing copolymer and the molded article. Another object is to provide a molded article.